Generally many hard surface detergent compositions, and in particular automatic dishwashing detergent compositions, have an alkaline pH, usually in the range of from 9 to 12. It is well known to use a bleach system in such compositions in order to remove bleachable stains such as tea and tomato. For example automatic dishwashing detergent compositions comprising a peroxygen bleaching compound and a bleach activator are disclosed in EP-A-677576. Typical bleach systems used in such compositions include chlorine based bleaches and peroxygen bleaches, the latter being usually used with a bleach activator. Examples of the latter type of bleach system include percarbonate or perborate bleaches used with a bleach activator which is typically TAED. Indeed these two bleach/activator systems are the ones typically used in current detergent compositions.
However, if the pH of the composition is lowered to a more neutral pH, such as pH 7 or 8, the currently used standard chlorine or peroxygen bleaches are no longer effective. Their activation is kinetically hindered at these lower pHs and the oxidation processes thus proceed more slowly with the result that in order to provide the required bleaching effect several hours or even days is required instead of minutes which is the case at pHs of 9 and above. It has been suggested to use N-acyl and O-acyl bleach activator compounds to generate peroxy acids in aqueous acidic environments for bleaching properties in hard surface cleaners (see WO95/21236). It has also been suggested to use a pH adjustment system in automatic dishwashing compositions to obtain compositions which have an end pH of less than 10 (see WO95/12656 and WO 96/05283).
In some instances however it is desirable to formulate hard surface cleaners, and especially automatic dishwashing detergents, at lower pHs. This may apply for example where the detergent compositions are to comprise ingredients which are at least partially unstable at higher pHs, where it is desired to provide detergents which are less irritating to skin and eyes or where a lower pH composition is desired for some other reason.
To improve the bleach performance at pHs lower than 9, and especially at neutral pHs such as 7, an oxygen based bleach which is effective at this lower pH can be used. Monopersulphate salts, such as potassium peroxymonopersulphate (hereinafter KMPS) is one such peroxygen bleach which can be used.
However, even KMPS requires the use of a bleach activator in order to increase its activity to a level whereby acceptable bleaching is achieved at the required temperatures and in the required time.
KMPS has found use as a bleaching agent in denture care applications as disclosed in EP-A-787 482 where KMPS is used with TAED as an activator. The example in EP-A-787 482 comprises 20% wt KMPS, 3% wt sodium percarbonate and 1% wt TAED and requires an overnight reaction time in order to obtain excellent bleaching effects. Thus, the combination of KMPS and TAED is not suitable for low temperature bleaching where the reaction times have to be relatively short as is the case with hard surface cleaners, and especially so for automatic dishwashing compositions.
Other known activators for KMPS include ketones. It is known that the simplest ketone available, acetone, acts as an activator for KMPS; see W. Adam: Dioxiranes, “A new class of powerful oxidants”, JACS, 1989, p. 205 wherein it is disclosed that dioxirane is the intermediate, highly active, molecule which can be used for oxidising (bleaching) stains, food residues and the like. However, acetone is generally not desired as an ingredient of hard surface cleaners, and especially automatic dishwashing compositions as it presents a fire/explosion hazard and has an overpowering and distinctive smell which is very difficult to disguise.
Additional ketone activators for peroxygen bleaches, including KMPS, are disclosed in U.S. Pat. No. 3,822,114. Fabric and hard surface bleaching at pH 10 or above is disclosed.
EP 1 209 221 discloses certain cyclic sugar ketones for use as bleach activators, especially for use with peroxygen bleaches such as KMPS in compositions at pH 9 and 10. However, these bleach activators have been found to exhibit reaction times with the aforementioned bleaches of several hours and this is unacceptable or undesirable for hard surface cleaning detergent compositions. The bleach systems disclosed in EP 1 209 221 are only effective at pH 10 and above.
However, a disadvantage which exists with the prior art bleaching systems of monopersulphate salts and the disclosed ketone bleach activators is that their bleaching performance is not fully satisfactory as it either proceeds too slowly and/or is not effective enough and/or it is not effective at pHs of 9 or below.
It is an object of the present invention to address one or more of the above-mentioned problems. In particular, it is an object of the present invention to provide safe, reliable hard surface detergent compositions which exhibit effective removal or reduction of bleachable stains yet which have a pH of below pH 9, and furthermore which preferably do so in reaction times of less than 10 hours. It is a further object of the present invention to provide hard surface detergent compositions which exhibit good bleaching properties (in terms of efficacy and speed) at pH 6 to 8. It is still a further object of the present invention to provide such detergent compositions which provide based on either an aqueous system or one comprising an organic solvent solution. Most detergents are aqueous based systems and these require a buffering system to maintain the pH within the ranges of the present invention.